The present invention relates to sewing machine speed control systems, and in particular to a digital sewing machine speed control system in which machine speed is controlled in response to a digital speed setting signal. This invention is particularly advantageous for adaptation to microcomputers and also to manual selection of a desired operating speed characteristic to meet the operating conditions and to the operator's skill.
Conventional sewing machine speed control systems include an analog circuit that generates an analog-speed setting signal in response to the amount of depression of an operator-controlled foot pedal. The analog speed setting signal is typically generated by a magnetic flux sensor located with respect to a permanent magnet which is mounted for movement with the foot pedal, whereby the depression of the pedal results in a variation in the amplitude of the output of the magnetic flux sensor.
It is of particular importance to the proper functioning of industrial sewing machines that the sewing machine speed be closely controlled in response to incremental changes in pedal depression. Furthermore, it is desired that the sewing machine have a particular speed varying characteristic for each operating condition. It is further desired that the foot pedal depression versus speed characteristic be optimized for the level of skill and the specific needs of the operator.
However, it is almost impossible for conventional analog speed control system to achieve precision speed control as well as manual selection of operating characteristics. Further, the analog system is not adaptable to integrated-circuits and to microcomputer applications.
Copending U.S. patent application No. 199,704 filed Oct. 23, 1980 by the same applicants as the present invention, now U.S. Pat. No. 4,386,301, discloses a sewing machine speed control system having a position detector for generating a binary code in response to the amount of depression of foot pedal, manually operated switches, and a read only memory for generating a speed control signal in response to the position indicating binary code and to the operating states of the switches.